The present invention is directed to a process for the polymerization of butadiene-1,3 in which the amount of benzene used as polymerization diluent is significantly reduced.
The art is replete with examples of catalyst systems for the polymerization of butadiene-1,3. Free radical emulsion polymerization systems have been long known but the product has not been acceptable for use in the manufacture of tires for a variety of reasons. The development of the solution polymerization processes is well known. One such system uses an alkyl lithium, generally butyl lithium, polymerization initiator. Two distinct systems using Ziegler catalysts have been developed and adopted commercially. One Ziegler system uses titanium compounds in combination with aluminum alkyl compounds and the other system utilizes cobalt compounds in combination with aluminum alkyl compounds. Early disclosures connected with the use of the Ziegler catalysts taught that almost any hydrocarbon solvent could be used as the polymerization diluent although the only materials actually exemplified were benzene, toluene and benzene-butene mixtures. Commercial development of the systems was based on the use as diluent of benzene alone or mixed with butene, especially butene-1, because of the high polymerization rates achievable and the relative ease of removal of the diluents from the polymer.
Much more recently, concern has been raised as to the desirability of having even very low levels of benzene vapor in the working atmosphere. Because of the mechanical, technical and cost problems associated with the elimination of low levels of benzene from both the work environment and the polymer, it is desirable to reduce or eliminate benzene from the diluent system.